1. Field of the Invention
Processes for the continuous removal of products from high pressure systems do not currently exist. An effective means of maintaining high pressures in a reaction vessel while at the same time transferring products to atmospheric pressure without interrupting the process or materially reducing particle sizes is not currently known. Supercritical or high pressure processes are therefore usually performed batchwise since the methods are not available for removing the products continuously. For example, the precipitation of proteins and other compounds from solution is a useful separation technique, and high pressure carbon dioxide has been shown to be an effective means of achieving precipitation, but the continuous removal of the precipitated products has not been possible.
This invention relates to a novel process for the continuous removal of products from high pressure systems. In particular, a novel process for the continuous production of proteins by a high pressure carbon dioxide process is disclosed.
2. Description of the Prior Art
It is well known that the addition of acids, such as hydrochloric acid or sulfuric acid, to protein-containing solutions affects pH, thus precipitating any proteins in solution. Other factors such as ionic strength, dielectric properties of the solvent and temperature also affect the solubility of proteins, and these factors can also be taken advantage of for precipitation purposes.
For example, the manufacture of acid casein may occur through the action of lactic acid-producing bacteria or the acidification of skim milk by a mineral acid such as HCl. In either case, acid casein precipitates at the isoelectric point of pH 4.6 and approximately 40.degree. C., conditions at which the negative charges on the surface of the casein micelles are neutralized (Bloomfield and Mead, 1975; West, 1986).
Jordan et al. (1987) have shown that it is possible to precipitate casein by dissolution of carbon dioxide in milk. The reversible reaction for the dissolution of carbon dioxide in water or milk is: EQU CO.sub.2 +H.sub.2 O.revreaction.HCO.sub.3.sup.- +H.sup.+
Increasing the pressure of carbon dioxide injected into the milk results in an increased production of H.sup.+ thereby lowering pH and causing coagulation of the protein.
Although it is known that proteins are precipitable by CO.sub.2 under high pressure, the process has to date been carried out batchwise because of the loss of pressure accompanying the removal of the products, i.e. protein solids. A search has gone on, however, for an effective method of producing proteins continuously so that the machinery involved does not have to go through a shut down/start up cycle, as is required for the precipitation in batches. In addition, high pressure batch processes are slow, impractical and add significantly to the cost of processing, and only small amounts of a product material can be obtained. Casein yields, for example, are only 13% (w/w) of the initial batch liquid on a wet basis.
All high pressure systems reported to date use metering or needle valves to maintain system pressure and remove precipitated or extracted materials after depressurizing the system. Thus neither solid nor liquid components can be effectively removed continuously.